Retransmission methods of a wireless communication system exemplarily include a hybrid automatic retransmit request (HARQ) scheme for using combining a retransmitting scheme in a media access control (MAC) and link performance in a physical (PHY) layer link performance. The HARQ scheme restores received data by combining the transmitted data's receiving information and retransmitted data. The HARQ method includes a synchronous scheme and an asynchronous scheme.
Since the synchronous HARQ scheme generates retransmission in a predetermined time interval in, it needs no retransmission information or less information thereof to reduce an overhead of a downlink control signal. In addition, since the synchronous HARQ scheme efficiently controls a sleep mode, it is easy to reduce power consumption. However, since the synchronous HARQ scheme limits dynamic allocation for radio resources, it gives poor dynamic scheduling gain. On the contrary, the asynchronous HARQ scheme allows dynamic scheduling, and so the scheduling gain is increased but the allocation overhead occurs.
When an HARQ feedback channel is a physical channel in the HARQ process, a cyclic redundancy checking (CRC) of the MAC layer may not be used. In this case, the HARQ feedback channel may generate an error. That is, when a terminal transmits a negative acknowledge (NAK) through a feedback channel in the downlink HARQ data transmission process, a base station may mistakenly receives it as an acknowledge (ACK) to generate a NAK to ACK error. The NAK to ACK error may cause data loss or may generate a long delay until a transmitting side recognizes it and retransmits data.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.